Compatibility summary
Your Singapore plug may fit in Saint Kitts and Nevis outlets, as both use at least one common plug type.
Plug comparison
Singapore plug types: G
Saint Kitts and Nevis plug types: A B G
Both countries share at least one plug type (G and A B G), so some plugs may work without an adapter. Check your appliance.
Voltage comparison
Singapore: 230V, 50Hz
Saint Kitts and Nevis: 230V, 60Hz
Voltage difference is within a range many devices tolerate; check your appliance label.